In recent years, the substantial increases in the energy costs of heating and cooling has encouraged the development of new and better insulation materials and many new insulation materials have been developed in an attempt to satisfy this need. The same increases in energy costs have provided an incentive for adapting solar energy as a means for providing heating and cooling. The attempts to adapt solar energy for these uses would become more practical with the development of improved and more efficient insulating materials.
In recent years, the substantial increases in costs of basic materials such as plastics, cement, asphalt and the like has also encouraged development and use of filler materials to reduce the amount and cost of the basic materials used and the weight of the finished materials. One of the newly suggested filler materials utilizes hollow glass microspheres. The known methods for producing hollow glass microspheres for use as filler materials, however, have not been successful in producing microspheres of uniform size or uniform thin walls which makes it very difficult to produce filler and insulation materials of controlled and predictable physical and chemical characteristics and quality.
One of the newly developed insulation materials utilizes packed glass microspheres, the outer surface of which microspheres are coated with a reflective metal and a vacuum is maintained in the interstices area between the microspheres. The outer reflective metal coating minimizes heat transfer by radiation and a vacuum maintained in the interstices area minimizes heat transfer by gas conduction. Insulation materials, however, made from these types of microspheres possess several inherent disadvantages. It has been found to be difficult if not impossible in many applications to maintain the vacuum in the interstices area between the packed microspheres and loss of this vacuum increases the heat transfer by gas conduction. It has also been found very difficult and costly to deposit a relatively thin uniform film of reflective metal on the outer surface of the microspheres. Even where a suitable thin reflective coating of metal has been deposited on the outer surface of the microspheres, it is found that as the coating wears the area of point to point contact between the microspheres increases which increases heat transfer by solid conduction between the mircrospheres and the wearing of the reflective metal coating necessarily causes deterioration of the reflective metal surface and further increases heat transfer by radiation.
The known methods for producing hollow glass microspheres have not been successful in producing microspheres of relatively uniform size or uniform thin walls which makes it very difficult to produce insulation materials of controlled and predictable characteristics and quality.
One of the existing methods of producing hollow glass microspheres for use as insulating materials, for example, as disclosed in the Veatch et al U.S. Pat. No. 2,797,201 or Beck et al U.S. Pat. No. 3,365,315 involves dispersing a liquid and/or solid gas-phase precursor material in the glass material to be blown to form the microspheres. The glass material containing the solid or liquid gas-phase precursor enclosed therein is then heated to convert the solid and/or liquid gas-phase precursor material into a gas and is further heated to expand the gas and produce the hollow glass microsphere containing therein the expanded gas. This process is, understandably, difficult to control and of necessity, i.e. inherently, produces glass microspheres of random size and wall thickness, microspheres with walls that have sections or portions of the walls that are relatively thin, walls that have holes, small trapped bubbles, trapped or dissolved gases, any one or more of which will result in a substantial weakening of the microspheres, and a substantial number or proportion of microspheres which are not suitable for use and must be scrapped or recycled.
Further, the use of conventional fiberglass insulation is being questioned in the light of the recently discovered possibility that fiberglass of certain particle size may be carcinogenic in the same or similar manner as asbestos. The use of polyurethane foams, urea-formaldehyde foams and polystyrene foams as insulating materials have recently been criticized because of their dimensional and chemical instability, for example, a tendency to shrink and to evolve the blowing gases such as Freon and to evolve unreacted gases such as formaldehyde.
In addition, in some applications, the use of low density microspheres presents a serious problem because they are difficult to handle since they are readily elutriated and tend to blow about. In situations of this type, the filamented microspheres of the present invention provide a convenient and safe method of handling the microspheres.
It is also been suggested that hollow glass vacuum microspheres having a reflective metal deposited on the inner wall surface thereof be used to make insulating materials. There have been several methods suggested for making this type of hollow vacuum microsphere but to date none of the known methods are believed to have been successful in making any such microspheres.
Further, the existing methods practiced to produce hollow glass microspheres usually rely on high soda content glass compositions because of their relatively low melting points. These glass compositions, however, were found to have poor long term weathering characteristics.
Thus, the known methods for producing hollow glass microspheres have therefore not been successful in producing microspheres of uniform size or uniform thin walls or in producing hollow glass microspheres of controlled and predictable physical and chemical characteristics, quality and strength.
In addition, applicant found in his initial attempts to use an inert blowing gas to blow a thin molten glass film to form a hollow glass microsphere that the formation of the glass microsphere was extremely sensitive and that unstable films were produced which burst into minute sprays of droplets before a molten glass film could be blown into a microsphere and detached from a blowing nozzle. There was also a tendency for the molten glass fluid to creep up the blowing nozzle under the action of wetting forces. Thus, initial attempts to blow hollow glass microspheres from thin molten glass films were unsuccessful.
The attempts to use solar energy for heating and/or cooling have been hampered by the rapid increase in rate of heat loss to the surrounding atmosphere that occurs when the outside temperature is below 32.degree. F. or when the operating temperature, i.e. outlet heat exchange medium of the solar energy collector, approaches 160.degree. F. The lower the outside temperature or the higher the operating temperature of the solar energy collector, the greater the heat loss and the lower the efficiency of the solar collector. It has been found that with the commercially attractive insulation technology available that reasonably priced solar collectors have only been operated efficiently at outside temperatures above 32.degree. F. and at operating temperatures below 160.degree. F. Though this is sufficient for heating hot water for bathing and laundry uses and for providing household heat, it is not sufficient for heating at outside temperatures below 32.degree. F. or for air-conditioner applications.